The technique chosen to manufacture a multi-component printed circuit board such as those typically found in computer and similar high density digital circuit applications, depends upon the number of such boards to be generated in a single production run. Where only a few boards are intended, the technique of wire-wrapping is typically employed. Here the electrical leads of components, such as individual or integrated circuit elements, are installed into sockets which have wiring pins or leads passing through apertures in a printed circit board to the opposite side. The pins are subsequently interconnected by wire-wrap techniques. For very large numbers of production runs, into the hundreds or more, multi-layer board techniques are typically employed. Here, despite the high density of component connections, the number of lead crossings can, by careful planning, be reduced to a number compatible with the use of a plurality of, for example ten, layers of circuit board wiring patterns, each insulated from the other and accessible from one or the other circit board sides by through-plated connections.
There exists a large number of circuit board applications for which the production numbers fall between these two extremes. One previous technique for producing printed circuit boards in this middle area includes an automated wiring technique in which the leads of components to be installed are typically shortened and bent to permit them to be soldered to respective terminal pads on one surface of a printed circuit board. Through-plating techniques provide electrical connection from these printed circuit pads on the component side of the circuit board to terminal pads on the opposite side of the circuit board. These circuit pads, on the opposite side of the circuit board, are then typically interconnected in the desired pattern using an automated interconnect system. One such system is the BONDEX system of the assignee of the present application, Augat, Inc., Mansfield, Mass. This system is represented in U.S. Pat. No. 3,840,169. Other automatic wiring systems are known.
In this prior technique the components and wiring are located on opposite sides of the printed circuit board in order to prevent the wiring network from interfering with the installation and placement of the electrical components, and vice versa. Wave soldering is not applicable to such circuit boards because with the components located on one side of the circuit board and the wiring done on the other side, there is no free side that can be wave soldered. Great efficiency is produced by the automated wiring technique, however, even though the component installation on the opposite side of the circuit board typically proceeds by more time consuming individual connection soldering operations.